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Cyclic AMP‐and beta‐agonist‐activated chloride conductance of a toad skin epithelium.
Author(s) -
Willumsen N J,
Vestergaard L,
Larsen E H
Publication year - 1992
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1992.sp019106
Subject(s) - isoprenaline , chemistry , intracellular , transepithelial potential difference , biophysics , forskolin , membrane potential , conductance , chloride , amiloride , endocrinology , ion transporter , sodium , medicine , stimulation , membrane , biochemistry , biology , combinatorics , receptor , mathematics , organic chemistry
1. The control by intracellular cyclic AMP and beta‐adrenergic stimulation of chloride conductance was studied in toad skin epithelium mounted in a chamber on the stage of an upright microscope. Impalement of identified principal cells from the serosal side with single‐barrelled conventional or double‐barrelled Cl(‐)‐sensitive microelectrodes was performed at x500 magnification. For blocking the active sodium current 50 microM‐amiloride was present in the mucosal bath. 2. When clamped at transepithelial potential difference V = 0 mV, the preparations generated clamping currents of 0.9 +/‐ 1 microA/cm2 (mean +/‐ S.E.M.; number of observations n = 55). The intracellular potential of principal cells (Vb) was ‐96 +/‐ 2 mV with a fractional resistance of the basolateral membrane (fRb) of 0.016 +/‐ 0.003 (n = 54), and an intracellular Cl‐ activity of 40 +/‐ 2 mM (n = 24). 3. At V = 0 mV, serosal application of a cyclic AMP analogue, dibutyryl cyclic AMP (500 microM) or a beta‐adrenergic agonist, isoprenaline (5 microM) resulted in a sixfold increase in transepithelial Cl‐ conductance identified by standard 36Cl‐ tracer technique. 4. The clamping current at V = 0 mV was unaffected by cyclic AMP (short‐circuit current Isc = 0.1 +/‐ 0.3 microA/cm2, n = 16) indicating that subepidermal Cl(‐)‐secreting glands are not functioning in our preparations obtained by collagenase treatment. 5. Cyclic AMP‐ or isoprenaline‐induced chloride conductance (Gcl) activation (V = 0 mV) was not reflected in membrane potential and intracellular Cl‐ activity in principal cells. Intracellular chloride activity was constant at approximately 40 mM at membrane potentials between ‐90 and ‐100 mV. Therefore, it can be concluded that the principal cells are not contributing to activated Cl‐ currents. 6. At V = ‐100 mV where the voltage‐dependent chloride conductance of mitochondria‐rich (MR) cells was already fully activated, GCl was unaffected by cyclic AMP or isoprenaline. The major effect of these treatments was a rightward displacement of the MR cell‐generated GCl‐V relationship along the V axis. 7. Our results indicate that the beta‐adrenergically controlled cyclic AMP‐mediated chloride conductance is localized to the mitochondria‐rich cells.